Foam cups with enhanced coffee retention

ABSTRACT

Enhanced coffee retention properties are achieved in thermoplastic polymer foam cups molded from thermoplastic polymer particles by coating at least a portion of the surfaces of the particles before molding with a fluorosurfactant.

This invention relates to molded thermoplastic foam cups.

More specifically, this invention pertains to molded thermoplastic foamcups which exhibit enhanced coffee retention properties.

The manufacture of molded articles, e.g., cups from expandedthermoplastic particles is well known. The most commonly usedthermoplastic particles are expandable polystyrene beads known as EPS.Typically, polystyrene beads are impregnated with a blowing agent whichboils below the softening point of the polystyrene and causes theimpregnated beads to expand when they are heated. When the impregnatedbeads are heated in a mold cavity, they expand to fill the cavity andfuse together to form a shaped article.

The formation of molded articles, e.g., cups from impregnatedpolystyrene beads, is generally done in two steps. First, theimpregnated polystyrene beads are pre-expanded to a density of fromabout 2 to about 12 pounds per cubic foot. Second, the expanded beads or"prepuff" are heated in a closed mold to further expand the prepuff andto form a fused article having the shape of the mold. The second step isgenerally referred to as "molding."

The pre-expansion step is conventionally carried out by heating theimpregnated beads using any conventional heating medium such as steam,hot air, hot water, or radiant heat. One generally accepted method foraccomplishing the pre-expansion of impregnated thermoplastic particlesis taught in U.S. Pat. No. 3,023,175 to Rodman.

In the manufacture of foam cups, the preferred thermoplastic isexpandable polystyrene beads. The polystyrene beads used to make foamcups are generally prepared by an aqueous suspension polymerizationprocess which results in beads that can be screened to relativelyprecise bead sizes. Typically, bead diameters are within the range offrom about 0.008 to about 0.02 inch.

In spite of careful bead size control, one problem which continues toplague the molded cup industry is that cups molded from expandablepolystyrene beads exhibit a tendency to leak coffee. The leakage resultsfrom penetration of the coffee around the fused polystyrene beads. Thepresent invention provides a molded foam cup which exhibits exhancedcoffee retention.

According to this invention, it has been found that if at least aportion of the surfaces of the thermoplastic beads is coated with afluorosurfactant, cups molded therefrom exhibit enhanced coffeeretention as compared to cups molded from the same expandedthermoplastic beads in the absence of the fluorosurfactant coating.

In the practice of this invention, any suitable thermoplastichomopolymer or copolymer can be employed. Particularly suitable for useare homopolymers derived from vinyl aromatic monomers including styrene,isopropylstyrene, alpha-methylstyrene, nuclear methylstyrenes,chlorostyrene, tert-butylstyrene, and the like, as well as copolymersprepared by the copolymerization of at least one vinyl aromatic monomerwith monomers such as butadiene, alkyl methacrylates, alkyl acrylates,acrylonitrile, and maleic anhydride, wherein the vinyl aromatic monomeris present in at least 50% by weight of the copolymer. Styrenic polymersare preferred, particularly polystyrene.

The polymer used in this invention must be in the form of beads,granules, or other particles convenient for the expansion and moldingoperations. Beads formed from an aqueous suspension process areessentially spherical and are preferred for molding foam cups.

The polymer particles are impregnated using any conventional method witha suitable blowing agent. For example, the impregnation can be achievedby adding the blowing agent to the aqueous suspension during thepolymerization of the polymer, or alternatively by re-suspending thepolymer particles in an aqueous medium and then incorporating theblowing agent as taught in U.S. Pat. No. 2,983,692 to D'Alelio. Anygaseous material or material which will produce gases on heating can beused as the blowing agent. Conventional blowing agents include aliphatichydrocarbons containing 4 to 6 carbon atoms in the molecule, such asbutanes, pentanes, hexanes, and the halogenated hydrocarbons which boilat a temperature below the softening point of the polymer chosen.

Fluorosurfactants suitable for use to coat the expandable polymerparticles are represented by the following general formula:

    R--CH.sub.2 --X,

wherein R represents a perfluoroalkyl group having from 6 to 16 carbonatoms; wherein X represents --CH₂ SCH₂ CH₂ CO₂ Li, --CH₂ SO₃ H, --CH₂SO₃ NH₄, --CH₂ O(CH₂ CH₂ O)_(x) H, --CH₂ O(CH₂ CH₂ O)_(y) H, --CH₂ SCH₂CH₂ N⁺ (CH₃)₃ CH₃ SO₄ ⁻, --CH(OCOCH₃)CH₂ N⁺ (CH₃)₂ CH₂ CO₂ ⁻, and##STR1## and wherein x represents an integer from 8 to 14, y representsan integer from 4 to 7, R' represents --OCH₂ CH₂ R or --OM, and Mrepresents --H, --NH₄, or --NH₂ (CH₂ CH₂ OH)₂.

Fluorosurfactants having the above general formula are commerciallyavailable from E. I. DuPont under the trademark ZONYL®.

ZONYL fluorosurfactants grades FSA (50% solids), FSP (35% solids), FSE(10% solids), RP, NF, UR (100% solids), FSJ (40% solids), TBS (33%solids), FSN (40% solids), FSN-100 (100% solids), FSO (50% solids),FSO-100 (100% solids), FSC (50% solids), and FSK (47% solids) aresuitable for use in this invention. The ZONYL fluorosurfactants aretypically supplied in diluents. All amounts by weight of ZONYLfluorosurfactant listed herein are based on 100% solids unless statedotherwise. The typical diluents are water/ethylene glycol,water/isopropyl alcohol, or water/acetic acid. ZONYL FSP is preferredand is supplied as 35% solids in water/isopropyl alcohol (45:20)solution.

The fluorosurfactant can be coated onto the polymer particles using anysuitable method. For example, the fluorosurfactant can be applied byblending the polymer particles with the fluorosurfactant in a suitablemixer, e.g., a high intensity mixer, a low intensity ribbon blender, ora drum mixer. Alternatively, the fluorosurfactant can be applied duringthe impregnation of the polymer particles by adding it along with theblowing agent.

Enhanced coffee retention has been observed when as little as about 0.01part by weight fluorosurfactant (100% solids) is employed per each 100parts by weight of polymer particles. Using more than about 0.25 part byweight of fluorosurfactant (100% solids) has not been found to impartany significant enhancement in the coffee retention of molded cups.

Moreover, the entire surface of the particles does not need to becompletely coated. It is adequate for the purposes of this invention ifat least a portion of the surfaces of the particles are coated withfluorosurfactant. In the practice of this invention, thefluorosurfactant in diluent solution is coated on at least a portion ofthe surfaces of the beads, and the diluent is removed, leaving a thinfilm coating of the fluorosurfactant on the bead. The following examplesfurther demonstrate the invention.

EXAMPLE 1

This example demonstrates the preparation of fluorosurfactant coatedpolystyrene beads and foam cups produced therefrom. The polystyrenebeads were coated with fluorosurfactant by blending. Five samples (A-E)were separately prepared using the following procedure:

To 300 g of n-pentane impregnated polystyrene beads having beaddiameters within the range of from about 0.008 to about 0.02 inch wasadded the amount and type of fluorosurfactant shown in column 2 offollowing Table 1. The mixture of impregnated beads and fluorosurfactantwas tumble blended in a glass jar for about 15 minutes, and then about0.24 g of zinc stearate, a mold release agent, was added. The mixturewas further tumble blended for about a half hour.

The impregnated, fluorosurfactant-coated beads were pre-expanded in aBuccaneer expander to the density shown in column 3 of following Table 1and allowed to age for at least 2 hours before being molded into cups.

Cup molding was carried out using a 6 W smooth wall mold which producesa 6 oz. cup. The cup molding machine was set to a steam header pressureof 120 psi and a back pressure of 35 psi. The total molding cycle took6.43 seconds per cup and consisted of fill time 0.85 second, dwell time0.65 second, cook time 1.70 seconds, and cool time 3.25 seconds. Fortycups were molded from each sample and allowed to age overnight beforetesting.

Ten cups of each sample were subjected to coffee retention testing asfollows: Coffee at 190° F. was poured into each cup and the side wallsand bottom of each cup containing coffee was observed for coffee stainsor leakage every 15 minutes over a 2 hour period.

The mean time to failure (MTF) of each ten cup sample was calculated byadding the time to failure for each cup (the 15 minute period duringwhich a cup exhibits leakage or staining is recorded as the time tofailure for that cup) and dividing the total time by the number of cupstested. The maximum MTF value if none of the ten cups in a sampleexhibited any stain or leakage is 2.0 hours. The minimum MTF value ifall ten cups fail within the first 15 minutes is 0.25 hour.

Coffee retention testing was repeated on a second set and a third set often cups of each of the five samples 2 weeks and 1 month after the firsttest. The results of the coffee retention testing is set forth infollowing Table 1.

                  TABLE 1                                                         ______________________________________                                                                  Coffee Retention After                              Sam- Fluorosurfactant                                                                            Den-   Aging (MTF).sup.2                                   ple  (wt %)        sity   1 Day 2 Week 1 Month                                ______________________________________                                        Con- None          4.07   .sup. 0.43.sup.2                                                                    0.35   0.45                                   trol                                                                          A    ZONYL FSP.sup.1 (0.01)                                                                      4.03   0.43  0.35   0.50                                   B    ZONYL FSP (0.05)                                                                            3.86   1.75  1.00   1.30                                   C    ZONYL FSP (0.075)                                                                           3.94   1.88  1.70   2.00                                   D    ZONYL FSP (0.10)                                                                            3.87   1.58  1.85   2.00                                   E    ZONYL FSP (0.15)                                                                            3.59   1.27  0.88   0.80                                   ______________________________________                                         1. ZONYL FSP Fluorosurfactant is represented by the following formula:        ##STR2##                                                                      2. Mean Time to Failure of a ten cup sample in hours.                    

EXAMPLE 2

This example demonstrates the invention using substantially theprocedure of Example 1 and compares the difference in coffee retentionachieved using three different fluorosurfactants. Three samples (F-H)and a control were prepared.

The amount and type of fluorosurfactant used and the results of thecoffee retention testing are shown in following Table 2.

                  TABLE 2                                                         ______________________________________                                                                  Coffee Retention After                              Sam- Fluorosurfactant                                                                            Den-   Aging (MTF)                                         ple  (wt %)        sity   1 Day 2 Week 1 Month                                ______________________________________                                        Con- None          3.96   0.43  0.25   0.25                                   trol                                                                          F    ZONYL FSE.sup.1                                                                             3.77   0.48  0.45   0.40                                        (0.075)                                                                  G    ZONYL RP.sup.2 (0.15)                                                                       3.84   0.65  0.50   0.38                                   H    ZONYL FSP (0.15)                                                                            3.59   1.27  0.88   0.80                                   ______________________________________                                         1. ZONYL FSE Fluorosurfactant is nominally the same as ZONYL FSP (See         Example 1, Note 1).                                                           2. ZONYL RP Fluorosurfactant is represented by the following formula:         ##STR3##                                                                 

EXAMPLE 3

This example demonstrates another method for coating polystyrene beadswith fluorosurfactant and describes introduction of fluorosurfactantduring the impregnation of the polystyrene beads.

To a soda pop bottle containing 100 g of unimpregnated polystyrene beadshaving diameters within the range of from about 0.009 to about 0.03 inchis added about 97 ml of distilled water, about 2.0 g of a suspendingagent (tricalcium phosphate), about 2.0 ml of soap (sodiumdodecylbenzene sulfonate), about 0.3 g of a 35% fluorosurfactantsolution (ZONYL® FSP), and about 7.8 g of n-pentane blowing agent.

The contents of the bottle are tumbled end over end in an oil bath andheated to about 105° C. After remaining at 105° C. for about 2 hours,the contents are cooled to room temperature, the bottle is opened, andthe contents acidified to a pH of about 1.0.

The beads are retained in the acid for about 15 minutes, and then washedwith water, centrifuged, and tray dried for about 4 hours. The resultingbeads are recovered with at least a portion of their surfaces coatedwith fluorosurfactant and are tested for coffee retention according tothe procedure set out in Example 1. Cups molded from the resulting beadswhich are at least partially coated with fluorosurfactant exhibitenhanced coffee retention as compared to beads prepared identically butin the absence of the fluorosurfactant.

It will be evident from the foregoing that various modifications can bemade to this invention. Such, however, are considered as being withinthe scope of the invention.

What is claimed is:
 1. A method for enhancing the coffee retentivenessof molded foam cups made from foamable styrene polymer particles whichhave been impregnated with a blowing agent which comprises coating thethermoplastic polymer particles with an effective amount of afluorosurfactant having the general formula

    R--CH.sub.2 --X,

wherein R represents a perfluoroalkyl group having from 6 to 16 carbonatoms; wherein X represents --CH₂ SCH₂ CH₂ CO₂ Li, --CH₂ SO₃ H, --CH₂SO₃ NH₄, --CH₂ O(CH₂ CH₂ O)_(x) H, --CH₂ O(CH₂ CH₂ O)_(y) H, --CH₂ SCH₂CH₂ N⁺ (CH₃)₃ CH₃ SO₄ ⁻, --CH(OCOCH₃)CH₂ N⁺ (CH₃)₂ CH₂ CO₂ ⁻, and##STR4## and wherein x represents an integer from 8 to 14, y representsan integer from 4 to 7, R' represents --OCH₂ CH₂ R or --OM, and Mrepresents --H, --NH₄, or --NH₂ (CH₂ CH₂ OH)₂, said fluorosurfactantbeing present in sufficient quantity to retard the rate at which coffeeleaks through said molded foam cups as compared to the rate at whichcoffee leaks in the absence of said fluorosurfactant.
 2. The method ofclaim 1 in which said fluorosurfactant is employed in an amount fromabout 0.01 to about 0.25 part by weight (100% solids) per each 100 partsby weight of said foamable thermoplastic particles.
 3. The method ofclaim 1 in which the fluorosurfactant is coated on the styrene polymerparticles before the step of impregnating the particles with a blowingagent by blending.
 4. The method of claim 1 in which thefluorosurfactant is coated on the styrene polymer particles after thestep of impregnating the polymer particles with a blowing agent byblending.
 5. The method of claim 1 in which the fluorosurfactant iscoated on the polymer particles by introducing the fluorosurfactantduring the step of impregnating the styrene polymer particles with ablowing agent.